When routing a headerless fuel system should all lines pitch downhill
when plane is at 3pt (for H2o). I can get most lines to do that, but the
right rear tank line is a little up hill when heading to the valve.
The lines will plenty downhill when in flight.

Building a Smith , Thanks Jon

Crash

10-09-2004, 05:44 PM

They should always go downhill towards the gasolator sump, how else is water going to make it to the sump. One of the problems with 3" extended gear and 31" tires is the front of these Cubs is getting so high, that on the ground the RH tank line doesn't feed down hill anymore. I'am surprised the FAA hasn't caught it yet. Crash

diggler

10-09-2004, 10:37 PM

[delete

jon

10-10-2004, 12:10 AM

Yep Crash its not looking good. With 26" rubber things just got worse,
even routing the line high in the upper baggage area you cant get downhill to the valve. Im thinking of installing a tee and rear drain behind the baggage area, this looks to be the best solution.

Jon

Crash

10-10-2004, 12:36 AM

Come off the rear fitting of the RH tank and stay high. The one obstical that forces the line down is the "D" window channel, but stay up as tight as possible to it. Forget the stock fuel line tabs, relocate them upwards where they are too low and keep the slope going. Both lines from the RH tank should slope to the "T" mounted just above the fuel selector in. Take care. Crash

T.J.

10-10-2004, 02:40 AM

I had the same problem when I put the left door in my XP. I put a "T" in the low point of the line at the rear of the passenger seat and a drain valve just inside of the left longeron.

jon

10-27-2004, 08:16 AM

What are you using to bend alum. fuel line. The hardware store sells
a tube bender and is listed for seel and copper but not alum. Will a
simple spring bender work.

Steve Pierce

10-27-2004, 08:29 AM

Spring bender works best for me because of all the weird bends around tubing etc. I have used the others but always resort back to the spring type on fuel lines.

S2D

10-27-2004, 10:33 AM

Which tubing is required in Supercub? 5052-0 , 3003-0 , or ? I just made up new tubes using 3003 versatube. then got to thinking might be too soft if you guys are talking about using tube benders on it. But I just "feel" tested the original tubing and seems to be the same properties as 3003.

Can't state fact for the certified side of things...but 3/8" ..when smoothly fabricated... with proper size valves and fitting orfices generally produces over 25 to 35 GPH in fuel flow test on most high wings (sometimes more...and unfortunately :( sometimes less). To be legal you must have at least 150% of the engines max required fuel flow at take off power when gravity flow and 125% when running a pump. This is with the aircraft positioned in a max climb attitude (usually 15 to 18* nose high)...5 gallons in the tank and the fuel line removed at the carb (and including the strainer screen fitting). The line must be held at exactly the carb inlet height and the amount of fuel timed into a measured container to arrive at fuel flow. Anyone know max fuel flow on the O-360? O-320 is around 15.5 GPH so minimum fuel flow needed at test would be 23.25GPH

Cheers,
Wayne

T.J.

10-28-2004, 12:55 AM

delete

T.J.

10-28-2004, 01:21 AM

Original J3 fuel lines were 3SO which is the same as 3003.

S2D

10-28-2004, 08:37 AM

Just took a PA-11 apart had 2 tank system and all heavy copper lines. Wonder if that was legal? Guess it must have been, it flew for 35 yrs that way!

Jon B.

10-28-2004, 09:25 AM

The A&P/IA that I'm working with on my Champ project recently built a Super Cub from scratch (the owner bought a new fuse) for a customer. He used 5052 hard line for all the fuel lines and stated that the use of soft 3003 wasn't legal.

I'm using 3003 on the Champ, as that's what came off it. Some of the lines on the original were copper, and one piece went back in - from the valve to the gascolator.

Jon

S2D

10-28-2004, 10:26 AM

He used 5052 hard line for all the fuel lines and stated that the use of soft 3003 wasn't legal.
Jon

Ask him why. Maybe he has Pipers specs. Univairs tubes are 5052, but they couldn't say what the original specs were. All the original I checked felt way too soft for 5052.

T.J.

10-28-2004, 02:16 PM

delete

jon

10-28-2004, 06:16 PM

What is Cub Crafters using for line size. Crash, what size line did you use?

diggler

10-28-2004, 10:00 PM

delete

Ahmet Kamil

12-19-2004, 07:06 AM

why not add another checklist item, "lift the tail 1', and drain the fuel line" ?

KOZ

12-19-2004, 10:47 PM

I have built 2 Smith cubs this year with 180'S and used 3/8th 5052 tubing with no problems. Both had 2 doors so the tubing had quite a long run from the rear port to the engine. Also built a Skybolt with an I0540 300Hp engine using 3/8th 5052. Almost vertical takeoff performance with no problems. Just stay away from the 2024 hard stuff.

sekps

12-20-2004, 03:05 AM

For my headerless installation I used 3/8" 5052 and bent it with a simple tube bender from Sears.

Diggler is correct that both Cub Crafters and Penn Yan use 3/8" fuel line but require a "both" position on the fuel selector with a placard that states "Use Both for Take Off and Landings". They both also require pressure caps on the fuel tanks.

I ran standard fuel caps for most of the summer (have a set of each). I tried everything I could to get the engine to starve for fuel and could not get it to even cough. Hard take off's on one tank, left and right. Radical manuvers on one tank or the other, and nothing. I did get it to quit when I ran on the right tank down to about 3 gallons then did a slow, coordinated steep turn with that wing low. Right at about 360 degrees the engine quit. Went to the Left tank, restarted the engine then back to the Right and flew level for some time before it was finally out. Take care. Crash

Ron B.

12-20-2004, 06:58 PM

Not quite on the same topic but still fuel related, what type of line 1/8" o.d. is used on the primer line ? I see Aircraft Spruce advertises a polyurethane line, is this the line used? Also quite a difference in price for the primer pumps listed,is it worth the difference? I'm building a Smith's with a 0-360.
Thanks Ron

Crash

12-20-2004, 07:58 PM

1/8" 2142 T1 .028 COPPER. Crash

Ron B.

12-20-2004, 08:12 PM

Thanks Crash
I didn't think plastic would be right but didn't see anything else listed. I'll locate some copper.
Thanks again
Ron

S2D

12-20-2004, 08:29 PM

Diggler is correct that both Cub Crafters and Penn Yan use 3/8" fuel line but require a "both" position on the fuel selector with a placard that states "Use Both for Take Off and Landings". They both also require pressure caps on the fuel tanks.

I ran standard fuel caps for most of the summer (have a set of each). I tried everything I could to get the engine to starve for fuel and could not get it to even cough. Hard take off's on one tank, left and right. Radical manuvers on one tank or the other, and nothing. I did get it to quit when I ran on the right tank down to about 3 gallons then did a slow, coordinated steep turn with that wing low. Right at about 360 degrees the engine quit. Went to the Left tank, restarted the engine then back to the Right and flew level for some time before it was finally out. Take care. Crash

any theories why Crash?? Tank unporting? Design of system with more than one G ?? I was going to test the gravity theory on my way home today, to see if something would fall straight to the floor or hit a side window first in a turn, but everytime I let go of the object it would hit the skylight , then bounce around and bean me on the head :roll: Will try it on a calm day. Still don't think a tank will unport in a coordinated constant altitude turn, but I may be all washed up.

Frank T

12-20-2004, 10:16 PM

What size is the smallest opening in the entire fuel system from the tank to carb? Seems like this is going to determine how much flow you are going to get using gravity only. Will 1/2 line provide any more flow than 3/8 if the hole in the fuel valve shaft is the same size as the ID of 3/8 tube. Maybe CRASH or someone else knows what size the opening in the fuel valve is, and can tell us.

Frank

Alaska Cubs

12-20-2004, 11:17 PM

This very topic was discussed a while ago on the Yahoo Stinson board when discussing the the use of the improved Allen 6S122 fuel selector valve, along with a JPI Fuel Scan 450. Both neck down to 3/8" while the 165 HP Stinsons' have 1/2" fuel lines. Bob H., an A&P and retired engineer wrote:
One of the fundemental concepts in the study of viscous flow in pipes holds that: The resistance to flow caused by a restriction is proportional to the length of the restriction and inversly proportional to the cube of the diameter of the restriction. There is about 9 feet of fuel line in a Stinson 108 so changing the whole system from 3/8 in. to 1/2 in. tubing would reduce the resistance to flow by a factor of 2.4:1. Adding in 3 or 4 inches of 3/8 in. restriction only reduces the total improvement by about 4%. Hardly enough to get excited about.
I hope this helps clear things up a bit.
Merry Christmas!!
Stan

Crash

12-20-2004, 11:17 PM

When you modify the fuel valve you use a 3/8" drill bit in the drill press. I am very picky and ream out all the ends I cut with a tubing cutter so they are not choked down. Any crimped tubing gets replaced. I would have to say it is pretty much 3/8" I.D. all the way through. The old Jensen STC required 1/2" tubing and looked like a real pain to work with. All of the fittings and ports in the gasolator are 3/8" anyway. The O-360 can't use that much more fuel then an O-320-B2B on take off so I don't see what the big deal is.

The O-360 is just an O-320-B2B with the pistons moving 5/8" further up and down the cylinders. Crash